Laboratory of Plant Molecular Physiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan.
Plant J. 2010 Feb;61(4):672-85. doi: 10.1111/j.1365-313X.2009.04092.x. Epub 2009 Nov 26.
A myriad of drought stress-inducible genes have been reported, and many of these are activated by abscisic acid (ABA). In the promoter regions of such ABA-regulated genes, conserved cis-elements, designated ABA-responsive elements (ABREs), control gene expression via bZIP-type AREB/ABF transcription factors. Although all three members of the AREB/ABF subfamily, AREB1, AREB2, and ABF3, are upregulated by ABA and water stress, it remains unclear whether these are functional homologs. Here, we report that all three AREB/ABF transcription factors require ABA for full activation, can form hetero- or homodimers to function in nuclei, and can interact with SRK2D/SnRK2.2, an SnRK2 protein kinase that was identified as a regulator of AREB1. Along with the tissue-specific expression patterns of these genes and the subcellular localization of their encoded proteins, these findings clearly indicate that AREB1, AREB2, and ABF3 have largely overlapping functions. To elucidate the role of these AREB/ABF transcription factors, we generated an areb1 areb2 abf3 triple mutant. Large-scale transcriptome analysis, which showed that stress-responsive gene expression is remarkably impaired in the triple mutant, revealed novel AREB/ABF downstream genes in response to water stress, including many LEA class and group-Ab PP2C genes and transcription factors. The areb1 areb2 abf3 triple mutant is more resistant to ABA than are the other single and double mutants with respect to primary root growth, and it displays reduced drought tolerance. Thus, these results indicate that AREB1, AREB2, and ABF3 are master transcription factors that cooperatively regulate ABRE-dependent gene expression for ABA signaling under conditions of water stress.
已报道了大量的干旱胁迫诱导基因，其中许多是由脱落酸（ABA）激活的。在这些 ABA 调控基因的启动子区域，保守的顺式元件，称为 ABA 响应元件（ABREs），通过 bZIP 型 AREB/ABF 转录因子控制基因表达。尽管 AREB/ABF 亚家族的三个成员 AREB1、AREB2 和 ABF3 均被 ABA 和水分胁迫上调，但它们是否为功能同源物尚不清楚。在这里，我们报告说，所有三种 AREB/ABF 转录因子都需要 ABA 才能完全激活，可以形成异源或同源二聚体在核中发挥作用，并可以与 SRK2D/SnRK2.2 相互作用，SRK2D/SnRK2.2 是一种被鉴定为 AREB1 调节剂的 SnRK2 蛋白激酶。结合这些基因的组织特异性表达模式及其编码蛋白的亚细胞定位，这些发现清楚地表明 AREB1、AREB2 和 ABF3 具有很大程度上的重叠功能。为了阐明这些 AREB/ABF 转录因子的作用，我们生成了 areb1 areb2 abf3 三重突变体。大规模转录组分析表明，三重突变体中应激响应基因的表达显著受损，揭示了水胁迫下新的 AREB/ABF 下游基因，包括许多 LEA 类和组-Ab PP2C 基因和转录因子。与其他单突变体和双突变体相比，areb1 areb2 abf3 三重突变体在主根生长方面对 ABA 的抗性更强，并且耐旱性降低。因此，这些结果表明，AREB1、AREB2 和 ABF3 是协同调节 ABRE 依赖性基因表达的主要转录因子，在水分胁迫条件下共同调节 ABA 信号。
